a + b = 11, a - b = 7 হলে, ab = কত?

a + b = 11, a - b = 7 হলে, ab = কত?

A 15

B 16

C 18

D 12

Solution

Correct Answer: Option C

4ab=(a+b) ²-(a-b ²)
       =   (11) ²-(7) ²
      =   121-49
      =72
∴ ab =72/4
∴ ab =18